1. Field of the Invention
This invention relates to electric field dependent/responsive fluids such as the so-called "electrorheological" or "electroviscous" fluids. More specifically, the invention relates to improved electric field dependent fluids and methods of preparing the same wherein the fluids exhibit a reversible viscosity rise in the presence of high voltage at temperatures in excess of 100 C. without the deleterious release of water. 2. Description of the Prior Art
It is generally known that electroviscous or electrorheological fluids exhibit pronounced changes in viscosity and resistance to shear in response to the application of an electric field. Such fluids generally comprises suspensions of finely divided, solid particles which intentionally contain a certain amount of adsorbed water dispersed in a nonconductive, hydrophobic liquid. The presence of the water has been acknowledged as being a critical and mechanistically necessary element in achieving the desired change in viscosity under the influence of an applied electric field. Thus for example U.S. Pat. No. 3,047,507 teaches and claims the addition of excess or adsorbed water as do U.S. Pat. Nos. 4,483,788; 4,033,892 and 4,129,513. In explaining mechanistically the role of adsorbed water it is postulated that the presence of adsorbed water in or on the particulate material is necessary to promote ionization and thus allow changes to move freely on the surface of the particles when an electric field is imposed. However, because of the intentional presence of adsorbed water in the electroviscous fluids of the prior art, such compositions are restricted to low temperature end use applications. In high temperature applications or in high shear rate applications wherein a shear induced exotherm can occur, free water or water vapor will be produced thus representing a potentially corrosive environment, which severely limits these prior art electroviscous fluid systems.